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Tests of Space Station’s Laser Downlink Successful

Photonics.comDec 2014
PASADENA, Calif., Dec. 15, 2014 — The first round of testing on an earth-to-orbit laser data link was a success, according to NASA officials.

In 18 tests over four months, the Optical Payload for Lasercomm Science (OPALS) system aboard the International Space Station transmitted text and video to a ground station. The laser system enabled much faster transmission than traditional radio-frequency methods.

“OPALS has shown that space-to-ground laser communications transmissions are practical and repeatable,” said Matthew Abrahamson, OPALS mission manager at NASA’s Jet Propulsion Laboratory. “As a bonus, OPALS has collected an enormous amount of data to advance the science of sending lasers through the atmosphere.”

An artist’s rendering of the OPALS system aboard the International Space Station. Courtesy of NASA/JPL-Caltech.
In its first test June 5, OPALS sent a copy of the same video (with the message, “Hello, World!”) every 3.5 s for 148 s. With traditional downlink methods, the 175-Mb video would have taken 10 minutes to transmit. In July, OPALS sent an HD video of the 1969 Apollo 11 moon landing.

“It took 12 hours to uplink the video using existing infrastructure, and OPALS downlinked it in just 7 s,” Abrahamson said.

The laser system communicates by locking onto a ground beacon emitted by the Optical Communications Telescope Laboratory’s ground station at JPL’s Table Mountain Observatory in Wrightwood, Calif.

The ground beacon uses four lasers to counter the effects of atmospheric turbulence. OPALS easily acquired the beacon under clear, dark conditions, Abrahamson said, but had more difficulty in daylight or when it was cloudy over Table Mountain. JPL is working on software and adaptive optics enhancements to counteract these problems, he said.